1. Field of the Invention
The present invention relates to a method of insulating a cathode ray tube used for electrical equipment having high voltage electrodes, in particular color television receivers, video and computer monitors, etc., applied to the insulation between stem pins to which a high voltage is supplied and to an electrical insulator composition for a cathode ray tube used for insulation between high voltage stem pins of a cathode ray tube and between other electrodes to which a high voltage is supplied.
2. Description of the Related Art
Generally, as shown in FIGS. 1B and 1C, a stem 20 is integrally attached to a neck of a cathode ray tube by fusing together the glass at is periphery and the glass around the end edge of the neck 1a. A stem base 30 is attached to the stem 20. The stem 20 is provided with a plurality of stem pins 21 at its periphery serving as electrodes in a predetermined pin circle shape and with a tip 22 projecting from its center portion. Note that the illustration of the stem pins 21 is omitted in FIG. 1C.
The stem base 30 is made of a polycarbonate or other plastic having an excellent insulating property and comprises, as shown in FIGS. 1A, 1B, and 2, a circular base 31, a tip holder 32 provided at the center portion of the base 31 for holding the tip 22 of the stem 20, a sector-shaped stem pin holder 33 provided on the base 31 in a state also serving as a part of a side wall of the tip holder 32 for holding the high voltage stem pins 21, and a skirt portion 34 extending downward from the peripheral edge of the base 31. The base 31 is formed, corresponding to the stem pins 21, with pin through holes 35 through which the stem pins 21 are inserted at the time of attaching the stem base 30 to the stem 20.
As a method of the related art for electrical insulation between the stem pins 21 of the stem 20 to which the stem base 30 is attached, a method of interposing an electrical insulator 40 shown in FIGS. 3A and 3B between the stem 20 and the stem base 30 as shown in FIG. 1B is known. The electrical insulator 40 is formed as a thick disk shape and is formed at its center portion with a tip through hole 41 for inserting the tip 22 of the stem 20. Further, pin through holes 42 through which all of the stem pins 21 including the high voltage stem pins are inserted at the time of placing the electrical insulator 40 on the stem 20 are formed corresponding to the stem pins 21.
The electrical insulator 40 is prepared by, for example in Japanese Unexamined Patent Publication (Kokai) No. 8-111191, extruding into a tape shape a viscous electrical insulator composition comprising 100 parts by weight of a silicone compound having an electrical insulation property plus 2 parts by weight of a silane coupling agent and 1.5 parts by weight of an organic peroxide (hereinafter referred to as the xe2x80x9cinsulator compositionxe2x80x9d) and punching out a disk shape using a die set. Further, Japanese Unexamined Patent Publication (Kokai) No. 7-94100 discloses a method of obtaining an electrical insulator by molding a viscous insulator comprising a silicone compound similar to the above publication into a flat plate of a large area and punching out disk shapes by a molding tool.
In both publications, first, the electrical insulator 40 shown in FIG. 4A is adhered to the back of the base 31 of the stem base 30 shown in FIG. 4B as shown in FIG. 4C. Then, the stem pins 21 are inserted through the pin through holes 42 of the electrical insulator 40 and the pin through holes 35 of the stem base 30 and the tip 22 is inserted through the tip through hole 41 of the electrical insulator 40 and the tip holder 32 of the stem base 30. In that state, the stem base 30 is attached to the stem 20 of the cathode ray tube 1, then pressed and heated to bond it so as to achieve electrical insulation between the stem pins 21.
Summarizing the problems to be solved by the present invention, in the inventions disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 8-111191 and 7-94100, however, since both punch out disk shapes from an insulator composition of a tape shape or a flat plate shape by a die set or a molding tool, the portion remaining after punching becomes wasted, that is, there is a disadvantage of a loss of the material loss.
Also, because the disk is produced by punching, it is difficult to mold the electrical insulator into a shape corresponding to a complicatedly shaped stem or stem base of a cathode ray tube. As a result, it ends up allowing air to become entrained between the stem base and the stem at the time of attaching the two. When air is entrained, disadvantages are caused such as a decline in the insulation property between the stem pins 21 due to the entrained air, an inability to draw out 100% of the electrical characteristics of the cathode ray tube, and insufficient bonding force between the stem and the stem base.
Note that since it is difficult to mold an electrical insulator into a complicated shape in the related art as explained above, an electrical insulator of substantially the same size as the base of the stem base has been prepared to provide insulation between all stem pins projecting from the stem. However, in actuality, it is possible to achieve sufficient electrical characteristics of the cathode ray tube by just insulation between the high voltage stem pins among the plurality of stem pins.
An object of the present invention is to provide a method of insulating a cathode ray tube enabling production of an electrical insulator without loss by efficiently using the electrical insulator composition.
Another object of the present invention is to provide a method of insulating a cathode ray tube enabling easy molding of an electrical insulator into a shape corresponding to a complicatedly shaped stem and stem base of the cathode ray tube by transfer molding and thereby enabling attachment of the stem base to the stem without entrainment of air.
A still other object of the present invention is to provide an electrical insulator composition for a cathode ray tube which is very effective in realizing a cathode ray tube improved in bonding of the stem and the stem base and improved in the insulation property between the high voltage stem pins by the above method of insulating a cathode ray tube.
According to a first aspect of the present invention, there is provided a method of insulating a cathode ray tube for insulation between stem pins using an electrical insulator when attaching to a stem, which is provided at the cathode ray tube and has a tip and stem pins projecting therefrom, an insulating stem base, which comprises a base through which pin through holes are formed and has provided projecting from the front surface thereof a tip holder, in a state with the stem pins inserted through the pin through holes and the tip held in the tip holder, comprising the steps of molding an electrical insulator composition comprising an uncured self-adhesive silicone rubber into a predetermined sheet shape by using a transfer mold to obtain an electrical insulator, arranging the electrical insulator in a state extending from the positions of the pin through holes on the back of the base of the stem base to the tip holder and adhering it to the back of the base, folding back the portion of the electrical insulator extending to the tip holder to the inside surface of the tip holder, and attaching the stem base to the stem.
According to the above aspect of the present invention, since an electrical insulator composition is molded by using a transfer mold (hereinafter the molding will be referred to as xe2x80x9ctransfer moldingxe2x80x9d) to obtain an electrical insulator, there is no loss of the electrical insulator composition such as when obtaining an electrical insulator by using a die set or molding tool. Also, due to the transfer molding, it becomes possible to easily mold the electrical insulator into a shape corresponding to the complicatedly shaped stem and stem base of the cathode ray tube. Further, since the electrical insulator is arranged in a state extending from the positions of the pin through holes toward the tip holder when adhering it to the back of the base of the stem base, and since the portion of the electrical insulator extending to the tip holder is folded back to the inside surface of the tip holder prior to attaching the stem base to the stem, the entrainment of air can be suppressed at the time of attaching the stem base to the stem.
According to a second aspect of the present invention, there is provided an electrical insulator composition for a cathode ray tube comprising an uncured self-adhesive silicone rubber, wherein the uncured self-adhesive silicone rubber comprises, with respect to 100 parts by weight of a silicone compound, 0.001 to 15 parts by weight of a bonding aid and 0.01 to 5 parts by weight of a vulcanization agent and has a Williams plasticity adjusted to 100 to 300.
According to the above aspect of the present invention, since 0.001 to 15 parts by weight of a bonding aid is added to the silicone compound, an electrical insulator composition achieving a bondability effectively and having an excellent releasability from the transfer mold when used for transfer molding can be obtained. Also, since 0.01 to 5 parts by weight of a vulcanization agent is added, an electrical insulator composition having an excellent rubber strength and enabling work using this electrical insulator composition to be performed with good work efficiency is obtained. Furthermore, since the composition is adjusted to a Williams plasticity of 100 to 300, the releasability from the transfer mold is excellent when using the electrical insulator composition for transfer molding and the composition can be easily molded into a complicated shape. Accordingly, an electrical insulator composition comprising a silicone compound to which an adhesive and vulcanization agent are added in the above ranges has an excellent releasability from a transfer mold, is easily molded into a complex shape, is easy to handle and is otherwise extremely suited to transfer molding, and has an excellent rubber strength.
According to a third aspect of the present invention, there is provided an electrical insulator composition for a cathode ray tube comprising an uncured adhesive silicone rubber, wherein the uncured adhesive silicone rubber comprises, with respect to 100 parts by weight of a silicone compound, 0.001 to 15 parts by weight of a bonding aid, 0.1 to 10 parts by weight of a cross-linking agent, and 0.0001 to 1 part by weight of a platinum compound and has a Williams plasticity adjusted to 100 to 300.
According to the above aspect of the present invention, since 0.001 to 15 parts by weight of a bonding aid is added to the silicone compound, an electrical insulator composition achieving a bondability effectively and having an excellent releasability from the transfer mold when used for transfer molding can be obtained. Also, since 0.1 to 10 parts by weight of a cross-linking agent is added, an electrical insulator composition having a predetermined hardness and an excellent insulation property can be obtained and, since 0.0001 to 1 part by weight of a platinum compound is added, an electrical insulator composition which cures by a suitable curing rate can be obtained. Further, since the compound is adjusted to a Williams plasticity of 100 to 300, the releasability from the transfer mold is excellent when using the electrical insulator composition for transfer molding and the composition can be easily molded into a complicated shape. Accordingly, an electrical insulator composition comprising a silicone compound to which bonding aid, cross-linking agent, and platinum compound are added in the above ranges has an excellent releasability from a transfer mold, is easily molded into a complex shape, is extremely suited to transfer molding, cures at a suitable curing rate, and has an excellent insulation property.